This is a continuation of studies to induced menstrual cycles in bilaterally ovariectomized rhesus monkeys. A series of daily injections containing varying amounts of estradiol, progesterone, and testosterone are given to the monkeys. Normal endometrial proliferation and differentiation occurs and menses is observed on day 1 or 2 following the 28th injection. The procedure allows for controlled, synchronized cycles in multiple monkeys and use of monkeys with seasonal cycles. It also allows for the investigator to predetermine the stage of the cycle for any given research precedure.